Hydraulic control system

ABSTRACT

Hydraulic control system producing parallel linkage of a toolholder located on control arms actuated by means of a hydraulic cylinder mechanically coupled between the toolholder and the control arms, the control units for said arms being allotted a hydraulic valve containing a supervisory unit detecting the movements of the arms and in dependence on the direction of movement of said arms, permitting the passage of fluid to a hydraulic unit allotted to said valve, said unit assuming a first position for the passage of fluid to one side of the cylinder on movement of the control arms in one direction under the influence of said fluid, and a second position for passage of fluid to the other side of the cylinder on movement of the control arms in the opposite direction.

United States Patent Gallo Ahlenlus i Oppange, Enlarger. Sweden [2|]AppLNo 829.655

[72] Inventor [54] HYDRAULIC CONTROL SYSTEM 13 Claims, 3 Drawing Figs.

[52] U.S.Cl n 9l/l70R. 60/S2HE.2l4/l40SL [5|] lnt.Cl .7 Ftllh U00, B66f9/00. F02f 3/62 [50] FleldolSe-rdr 2l4/I40.

[56] References Cited UNITED STATES PATENTS 2,8ll,265 l0/l957Wagner........................ 2l4/l40SL 2.914.202 ll/l959 WagnerPrimary Examiner- Edgar W. Geoghegan Arromey-Sughrue, Rothwell, Mion,Zinn 8t MacPcak ABSTRACT: Hydraulic control system producing parallellinkage of a toolholder located on control arms actuated by means of ahydraulic cylinder mechanically coupled betvveen the toolholder and thecontrol arms, the control units for said arms being allotted a hydraulicvalve containing a supervisory unit detecting the movements of the armsand in dependence on the direction of movement of said arms, permittingthe passage of fluid to a hydraulic unit allotted to said valve, saidunit assuming a first position for the passage of fluid to one side ofthe cylinder on movement of the control arms in one direction under theinfluence of said fluid, and a second position for passage of fluid tothe other side of the cylinder on movement of the control arms in theopposite direction HYDRAULIC CONTROL SYSTEM This invention relates to ahydraulic control system with angle transmitter to a hydraulic controlvalve, the transmitter working in dependence on the position of the toolholder. especially a control system for producing parallel linkage oftoolholders for cranes, loaders or the like.

On loading and excavating operations and the like with, for example,constructional machinery it is desirable that the tool of theconstructional machine can be made to assume a con stant angle with theunderlying surface during raising or lower ing of the booms supportingthe tool in order that material car ried by the tool shall not fall out.For this purpose simultane ous control of the vertical positions of thebooms and of the angular position of the tool in relation to the boomscan be effected manually from the driver's cabin of the constructionalmachine.

It is usual, however, that a lifting movement must be madesimultaneously with a rotary movement around an essentially verticalshaft or simultaneously with maneuvering of the machine. This involvesdifficulty in simultaneous manual supervision of the angular position ofthe tool in relation to booms, and so in relation to the ground surface.For this reason machines of these kinds are equipped with devices forautomatic parallel linkage of toolholders, and so of tools, during thelifting movement of the booms. These devices usually consist ofmechanical rods, slewing brackets and the like. But as the too] mustalso be usable for dumping and bending up in any position whatsoever ofthe booms, for example for unloading of the contents of the tool, suchdevices for parallel linkage of the tool are relatively complicated.They are also subjected to severe strains, so that rods, links, bearingsetc. must be robustly dimensioned. The costs of such devices aretherefore relatively high, and as they are also subjected to damageowing to their exposed positions, expensive stoppages occur.

As the devices for parallel linkage of the toolholder must be robustlydimensioned, and must be so designed moreover that the tool can be usedfor dumping and bending up irrespective of the positions of the booms,it is difficult to avoid that the parallel linkage devices involve somelimitation on the means for operation of the tool. This means that manyoperations take a longer time than if the maneuverability is unlimited.This has an unfavorable effect on the operating costs.

The present invention is intended to eliminate these draw backs and toprovide a cheap and reliable device which by simple means solves theproblem of parallel linkage of toolholders. The invention consists of ahydraulic control system for parallel linkage oftool holders arranged oncontrol arms actuated, for example, by means of hydraulic controlcylinders, preferentially on cranes, loaders or the like, comprising ahydraulic cylinder mechanically coupled between the toolholder and thecontrol arms and characterized chiefly in that the control units for thecontrol arms are allotted a hydraulic valve, comprising a supervisoryunit which detects the movements of the control arms, the supervisoryunit being arranged so as to permit the passage of fluid to a regulatingunit allotted to the hydraulic valve in dependence on the direction ofmovement of the control arms, and the regulating unit is arranged toassume a first position for the passage of fluid on movement of thecontrol arms in one direction under the influence ofthe fluid to oneside of the hydraulic cylinder and to assume a second position forpassage of fluid to the other side of the hydraulic cylinder on movementof the control arms in the opposite direction.

On hydraulically operated cranes, loaders and the like it is advisable,with the arrangement according to the invention, to use the fluid in thecontrol cylinders for control of the regulating unit and for regulationof the hydraulic cylinder of the toolholder. According to a furtherdevelopment of the invention it is proposed that the regulating unit andchannels in the hydraulic valve are so arranged that the hydrauliccylinder of the tool holder is supplied with pressure fluid when thetool is to be rotated counter to a force acting upon it but with returnfluid when the tool is to be rotated in the opposite direction. This isespecially advisable, for example, for tractors carrying a bucket on thebooms. When the booms are to be raised, this takes place counter to theforce of gravity due to the dead weight, tool and load, if any, in thetool, while the tool is being rotated in the same direction as theforces of gravity. The capacity of the hydraulic pump of the device canthereby be fully utilized for the lifting movement.

The conditions are reversed when the booms are to be lowered, whichtakes place under the influence of the forces of gravity, while the toolin such case is being rotated counter to the forces of gravity, thewhich rational movement at this stage is accordingly accomplished bymeans of pressure fluid.

For transmission of the relative positions of the toolholder and boomsto the supervisory unit it is suggested according to a furtherdevelopment of the invention that a Bowden cable or the like be arrangedin such a way that one end of the Bowden cable wire is coiled up on apulley rigidly connected to the toolholder, while the other end of thewire is taken to the supervisory unit via a pulley located at thepivoting axis of the booms on the machine. On raising of the booms, forexample, at a constant angle between them and the toolholder, the wireof the Bowden cable is coiled up on the pulley at the pivoting axis ofthe booms, whereby the wire, preferably against the ac tion of a spring,moves the supervisory unit a certain distance in the hydraulic valve. Inthis way, as described in greater detail below, communications areopened between different channels in the hydraulic valve in such a waythat the regulating unit is brought into action, with the result thatthe hydraulic cylinder of the toolholder is supplied with fluid forrotation of the toolholder, and so the tool, to the desired position.During this rotation of the tool the wire is uncoiled from the pulley onthe toolholder, so that the supervisory unit is returned to neutralafter the tool has assumed the desired position under spring action. Theactuation of the toolholder in the opposite direction when the booms arelowered takes place in the reverse manner.

With reference to the attached drawings one embodiment of the inventionwill now be described and other characteristics and advantages of adevice according to the invention will be demonstrated.

FIG. 1 shows a tractor with bucket attachment equipped with a deviceaccording to the invention,

FIG. 2 shows a hydraulic valve according to the invention,

FIG. 3 is a schematic diagram of the hydraulic connections between thehollow screws 2832 of the hydraulic valve [2 of FIG. 2 and the hydrauliccylinders 5 and I4 and control valve [0.

FIG. 1 shows a tractor equipped with a bucket attachment comprisingbooms 2 and a toolholder 3 on which is a bucket 4. The booms are raisedand lowered by means of hydraulic cylinders 5, the booms pivoting arounda shaft 6. The control cylinders 5 are actuated from a control valve 10by means of levers It. The bucket attachment is shown in two positions,a lowered position 2, 3, 4, S and raised position 2 3 4 5 With the tool4 at a given angle to the ground, accordingly, the booms 2, (2') and thetool holder 3, (3' assume different angles to one another depending onthe positions of the booms.

Above the control valve 10 there is a hydraulic valve I2 according tothe invention, from which fluid pressure lines 13 run to a hydrauliccylinder [4 between the boon is Z'and the toolholder 3. Furthermore, fortransmission of the movements of the booms 2 and of the angle at everyinstant between the booms 2 and the toolholder 3 to the hydraulic valve12 there is a Bowden cable 9 between the toolholder 3 and the hydraulicvalve 12. The wire l5 of the Bowden cable 9 is coiled up at one end on apulley 8 fixed to the toolholder 3 and at its other end, via a pulley 7located on the shaft 6 of the booms 2, is fixed to a supervisory unit inthe hydraulic valve 12. The wire 15 may, if necessary, be taken over anadditional pulley in order to obtain a suitabae direction in relation tothe supervisory unit. For raising of the bucket attachment, for examplefrom the position marked 2, 3, 4, to the position marked 2, 3', 4', 5',the wire ofthe Bowden cable 9 is coiled up round the pulley 7. If theangle between the booms 2 and the toolholder 3 remains constant duringthis movement, the position of the wire 15 at the toolholder is fixed,so that the wire 15 actuates the supervisory unit in such a way that thelatter is pulled in the direction out from the hydraulic valve. In thereverse manner the wire 15 is uncoiled from the pulley 7 when the booms2 are lowered, whereby the wire tension diminishes and falls to zero, asa result of which the supervisory unit is moved in the direction intothe hydraulic valve 12 under spring action. In this way impulses areobtained in the hydraulic valve 12, which, in the manner recountedbelow, result in the fact that the hydraulic cylinder 14 of thetoolholder 3 is caused to function in such a way that thc toolholder 3,and so the tool 4, is carried upwards or downwards, during the movementsofthe booms, at a constant angle with the ground.

FIG. 2 shows the various parts of the hydraulic valve [2 in detail. Thevalve contains, as mentioned, a supervisory unit having a control rod 16passing through most ofthe valve and, on the control rod, slottedclamping sleeves l8, 18', which are at least partly tapered. Thesupervisory unit also comprises a control plunger 17 which, by means oftapered shoulders 52, 52', is arranged to engage with the taperedsurfaces of the clamping sleeves l8, [8, The clamping sleeves l8, [8'are kept apart by the action of a compression spring 19. At one end ofthe control rod 16 there is a supporting washer 23 against which restsone end of a return spring 22, the other end of which rests against astop washer bearing on a shoulder in the valve housing. At the other endof the control rod [6 is a second stop washer 20'. The end of thecontrol rod [6 projecting from the valve housing is designed to beconnected to the wire 15 of the Bowden cable. Furthermore the idleposition of the control rod 16 relative to the valve housing isadjustable with a trimming screw 24.

For removal ofany fluid leakage around the control plunger 17 there aretwo chambers 36 and 4| around the control plunger 17 in the valvehousing which communicate with channels for return fluid in the valvehousing.

The hydraulic valve also comprises a regulating unit consist ing of aregulating plunger 25 having a hole passing through it axially. At oneend of the plunger 25 is a throttling disc 26 and at its other end aspring 27.

The hydraulic valve has also a number of fluid channels and five hollowscrews 28, 29, 30, 31, 32 passing through the valve housing forconnection both to the control valve 10 of the control cylinders 5 andto leads running to the control cylin ders 5 and the hydraulic cylinder14.

The hydraulic valve functions as follows.

On raising of the booms 2 pressure fluid from the control valve 10passes through the hollow screw 29 to the control cylinders 5 and returnfluid from the latter returns via the hollow screw 28 to the controlvalve 10. The screw 28, however, is not hollow throughout, but returnfluid is forced into a channel 34 down into a chamber 53 in thehydraulic valve 12, thence over to another chamber 54 and via a channel33 back into the hollow screw and on to the control valve 10. As soon asthis fluid flow for raising of the booms 2 has started, the control rod16 in the hydraulic valve [2 is drawn up, as described above, by thewire 15 owing to the movements of the booms and the coiling of the wirearound pulley 7. A chamber 40 around the control plunger 16 in thehydraulic valve 12 is thereby placed in open communication via a slot 43in the control plunger with another chamber 39 around the controlplunger 17. Through a channel 35 leading from chamber 53 around theregulating plunger 25 to chamber 39 some of the return fluid is therebyled via chambers 39 and 40 and a channel to a chamber 56 at the otherend of the regulating plunger 25. The fluid is thereby passed throughthe throttling disc 26 under a certain pressure, the throttlingproducing a pressure dif ference between the two sides of the throttlingdisc. The regulating plunger 25 is thereby moved against the action ofspring 27. The communication between chambers 53 and S4 is thus closed,while a communication is opened between chamber 53 and another chamber55. Return fluid from the control cylindcrs 5 can then freely flow intothe hollow screw 31 and thereafter through one of leads 13 to thehydraulic cylinder 14. Return fluid from the hydraulic cylinder 14 caneither be led via the hollow screw 32 and through channels not shown inthe drawing to the hollow screw 30 for return fluid or via adifferential piston valve, for example of the type described in ourSwedish Pat. and substitute therefor application No. 6614/65 whichcorresponds to US, Pat. No. 3,438,307, back to the pressure side of thehydraulic cylinder 14. The control fluid entering the regulating plungerthrough the throttling disc 26 is led off through holes 60 in theregulating plunger 25 into channel 59 leading to a chamber 48 and to thehollow screw 30 for removal of return fluidv As long as the hydrauliccylinder 14 is kept in working position in this way, the angle betweenthe tool holder 3 and the booms 2 changes and the wire 15 iscontinuously uncoiled from pulley 8. This uncoiling is compensated by acontinuous coiling up of the wire on pulley 7. If the angle between thetoolholder 3 and the boom 2 becomes too large, the wire slackens, theresult being that the supervisory unit is forced into the valve housingunder the action of the return spring 22. The communication betweenchambers 39 and 40 is then throttled so that the regulating plunger 25returns to neutral position under the action of spring 27. On loweringof the booms 2 pressure fluid flows in the reverse manner through thehollow screw 28 and return fluid returns through hollow screw 29. At theend ofthe hollow screw 29 facing the control valve 10 there is athrottling disc not shown in the drawing, which is displaccable underthe action of the prevailing fluid pressure. When the fluid flows in thedirection from the hydraulic valve 12 to the control valve 10, thisthrottling disc assumes throttling position. Some of the return fluid isthereby caused to flow out into channel 49, which leads to a thirdchamber 38 around the control plunger 17. As soon as the booms 2commence their downward movement, wire 15 is uncoiled from pulley 7, sothat the control rod 16, and therefore the control plunger 17, areforced into the valve housing under spring action. Chamber 38 is therebyplaced in communication with a fourth chamber 37 around the controlplunger via a channel 42 in the control plunger. The return fluid thenflows through channel 39, chamber 38, channel 42, chamber 37, a channel44 running from chamber 37 to chamber 40, and through channel 45 tochamber 56. Through the fact that throttling takes place at one end ofthe hollow screw 29, the return fluid has a rather higher pressure onlowering than on raising of the booms 2. The pressure difference betweenthe two sides of the throttling disc 26 thereby produces a movement ofthe regulating plunger 25 against the action of spring 27, which issufficient to open a communication between chamber 54 and anotherchamber 58 around the regulating plunger in the valve housing. Thedistance between chambers 54 and 58 is rather larger than betweenchambers 53 and 54. in the inner position of the regulating plunger,accordingly, a communication is open between chambers 54 and 58, whereasthe communciations between chambers 53 and 54 and between chambers 55and 53 closed. The pressure fluid through the hollow screw 28 can thennot flow into chamber 53 but is led entirely via chamber 58 out into achannel 50 leading from the latter to hollow screw 32. From hollow screw32 the pressure fluid then flows through one ofleads 13 to the hydrauliccylinder 14, whereby the toolholder is brought into parallel linkageduring the lowering of booms 2. The lowering of the booms thus takesplace under the influence of forces of gravity, while the entirecapacity of the fluid pump is utilized for upward rotation of the toolin relation to the booms.

Since, in this way no pressure fluid is supplied to the pressure side ofthe control cylinders, a nonrcturn valve 51 is provided in the valvehousing chamber 48 which communicates with hollow screws 30 for returnof hydraulic fluid to the control valve 10 and channel 35. As soon as anegative pressure arises in the side of each of the control cylinders 5which is to be filled with fluid during the lowering of booms 2, thenonreturn valve 51 opens and return fluid flows out chamber 48 andcontrol valve via channel 35, chamber 53 and channel 34 to controlcylinders 5. For tilting ofthe tool 4 the wire of the Bowden cable 9 isuncoiled from pulley 8, with the result that the wire is slackened andthat the control rod l6 is forced to its innermost position in the valvehousing under spring ac tion. The control plunger [7 is then in aposition such that chamber 37 communicates with chamber 38 and thereforewith channel 49. On a downward movement of the booms 2 the tool isimmediately bent up, the bending-up movement continuing until the wire15 has been coiled round pulley 8 so far that the wire is tensionedsufficiently to pull the control rod 16 slightly out of the valvehousing. By means of the trimming screw 24 the innermost position of thecontrol rod 16 can be regulated, which affects also the length of wirewhich, after tilting of tool 4, must be coiled around pulley 8 beforethe wire is tensioned. In this way it is possible to regulate theangular position to which the tool 4 is returned after tilting.

In the supervisory unit there are also stop washers 20, 20' and astrain-relieving sleeve 21. The function of these is to permit trimmingwith the trimming screw 24 and to render the valve inoperative in theevent that the control rod is subjected to too great a movement owing toa fault. If, for example, the control rod is pulled violently in thedirection out of the valve housing, the strain-relieving sleeve 21 isbrought up against the stop washer 20' and thus brings the slottedclamping sleeve 18 out of engagement with the shoulder 52. The controlrod is thus rendered freely movable in the control plunger 17.Correspondingly the clamping sleeve [8' can be taken out of engagementwith the shoulder 52' via the stop washer 20 in the event, for example,that the trimming screw 24 is unscrewed too far from the valve housing.

Through the fact that the control rod 16, and so the control plunger I7,is actuated by wire 15 of the Bowden cable 9, the stroke of the controlplunger increases during raising or lowering of the booms 2 in the eventthat the angle between toolholder 3 and booms 2 should remain constantor change too slowly owing, for example, to some inertia in theregulating plunger 25. A passage is thus opened still further betweenchambers 37 and 38 or 39 and 40 and additional control fluid is suppliedto the regulating plunger. An absence of reaction thus increases theaction of the valve, so ensuring reliable functioning of the hydraulicvalve. Furthermore manual con' trol of tool 4 is possible regardless ofthe position of booms 2 since the hollow screws 31 and 32 are incommunication with control valve 10 of the lifting attachment.

Although the invention has been described with reference to one of itsembodiments, it can be arbitrarily varied within the scope ofthefollowing claims.

What I claim is:

l. Hydraulic control system for producing parallel linkage of atoolholder located, for example, on control arms actuated by means ofhydraulic control cylinders, preferentially for cranes, loaders or thelike, comprising a hydraulic cylinder mechanically coupled between thetoolholder and the control arms, characterized in that the control unitsfor the control arms are allotted a hydraulic valve containing asupervisory unit detecting the movements of the control arms and, independence on the direction of movement of the control arms, permittingthe passage of fluid to a regulating unit allotted to the hydraulicvalve, the regulating unit assuming a first position for the passage offluid to one side of the hydraulic cylinder on movement of the controlarms in one direction under the influence of said fluid and a secondposition for passage of fluid to the other side of the hydrauliccylinder on movement of the control arms in the opposite direction.

2, Hydraulic control system according to claim 1, characterized in thatthe fluid let through by the supervisory unit to the regulating unitconsists of at least a part of the fluid of the control cylinders,preferentially the return fluid.

3. Hydraulic control system according to claim 1, characterized in thatthe fluid let through by the regulating unit to the hydraulic cylinderconsists of at least a part of the fluid of the control cylinders.

4. Hydraulic control system according to claim 3, charac terized in thatthe fluid let through by the regulating unit to the hydraulic cylinderon actuation of the toolholder in one direction against a force actingupon the toolholder carrying the tool consists of the pressure fluid ofthe control cylinders and, on actuation of the toolholder in theopposite direction, consists ofthe return fluid of the controlcylinders.

5. Hydraulic control system according to claim 1, wherein a shaft isoperatively mounted on each of said control arms and said toolholder,said control system characterized in that the supervisory unit isdesigned to be actuated by movements of the control arms via a Bowdcncable or the like, the wire of which passes over pulleys located on theshaft of the control arms and on the shaft of the toolholder.

6. Hydraulic control system according to claim 5, characterized in thatthe control unit contains a control plunger detachably located on andconcentric with a control rod and preferably spring-loaded.

7. Hydraulic control system according to claim 6, further comprising adetachable fitting connected to said control plunger of said controlrod, characterized in that the detachable fitting of the control plungerto the control rod is comprised of slotted clamping sleeves on thecontrol rod which have outer tapered shoulders for engagement with innertapered shoulders in the control plunger.

8. Hydraulic control system according to claim 7, charac terized in thatthe slotted clamping sleeves are designed, directly and/or viastrain-relieving sleeves located on the control rod in predeterminedlimit positions of the supervisory unit, to engage with stop washers inthe hydraulic valve for release of the engagement between the taperedshoulders on the clamping sleeves and the tapered shoulders in thecontrol plunger, and so to release the engagement between the controlrod and the control plunger in the said limit positions.

9. Hydraulic control system according to claim 1, characterized in thatthe supervisory unit has a trimming screw for adjustment of one limitposition of the control unit, thereby permitting, within certain limits,optional parallel linkage angles to which the toolholder is returnedafter tilting of the tool.

10. Hydraulic control system according to claim 1, characterized in thatthe regulating unit consists of a plunger, preferably acted upon by aspring, having at one end a hole passing axially through it andthrottled by a disc.

11. Hydraulic control system according to claim 1 characterized in thatthe hydraulic valve has hollow screws passing through it for pressurefluid and return fluid to and from the control cylinders of the controlarms and the hydraulic cylinder of the toolholder to permit manual ajustment of the positions of control arms as well as toolholder, saidhollow screws within the hydraulic valve having bushings leading tochannels in the hydraulic valve.

12. Hydraulic control system according to claim ll characterized inthat, between channels for return fluid in the hydraulic valve andchannels leading to one side ofthe control cylinders, there is anonreturn valve for the passing of fluid from the return channels to thecontrol cylinders on movement of the control arms in a directionessentially coinciding with the direction ofa force acting upon thetool.

13. Hydraulic control system according to claim 12, characterized inthat the hydraulic cylinder of the toolholder is allotted to adifferential piston valve for transmission of fluid from the suctionside to the pressure side of the hydraulic cylinder during movement ofthe tool in a direction essentially coinciding with the direction of aforce acting upon the tool.

1. Hydraulic control system for producing parallel linkage of atoolholder located, for example, on control arms actuated by means ofhydraulic control cylinders, preferentially for cranes, loaders or thelike, comprising a hydraulic cylinder mechanically coupled between thetoolholder and the control arms, characterized in that the control unitsfor the control arms are allotted a hydraulic valve containing asupervisory unit detecting the movements of the control arms and, independence on the direction of movement of the control arms, permittingthe passage of fluid to a regulating unit allotted to the hydraulicvalve, the regulating unit assuming a first position for the passage offluid to one side of the hydraulic cylinder on movement of the controlarms in one direction under the influence of said fluid and a secondposition for passage of fluid to the other side of the hydrauliccylinder on movement of the control arms in the opposite direction. 2.Hydraulic control system according to claim 1, characterized in that thefluid let through by the supervisory unit to the regulating unitconsists of at least a part of the fluid of the control cylinders,preferentially the return fluid.
 3. Hydraulic control system accordingto claim 1, characterized in that the fluid let through by theregulating unit to the hydraulic cylinder consists of at least a part ofthe fluid of the control cylinders.
 4. Hydraulic control systemaccording to claim 3, characterized in that the fluid let through by theregulating unit to the hydraulic cylinder on actuation of the toolholderin one direction against a force acting upon the toolholder carrying thetool consists of the pressure fluid of the control cylinders and, onactuation of the toolholder in the opposite direction, consists of thereturn fluid of the control cylinders.
 5. Hydraulic control systemaccording to claim 1, wherein a shaft is operatively mounted on each ofsaid control arms and said toolholder, said control system characterizedin that the supervisory unit is designed to be actuated by movements ofthe control arms via a Bowden cable or the like, the wire of whichpasses over pulleys located on the shaft of the control arms and on theshaft of the toolholder.
 6. Hydraulic control system according to claim5, characterized in that the control unit contains a control plungerdetachably located on and concentric with a control rod and preferablyspring-loaded.
 7. Hydraulic control system according to claim 6, furthercomprising a detachable fitting connected to said control plunger ofsaid control rod, characterized in that the detachable fitting of thecontrol plunger to the control rod is comprised of slotted clampingsleeves on the control rod which have outer tapered shoulders forengagement with inner tapered shoulders in the control plunger. 8.Hydraulic control system according to claim 7, characterized in that theslotted clamping sleeves are designed, directly and/or viastrain-relieving sleeves located on the control rod in predeterminedlimit positions of the supervisory unit, to engage with stop washers inthe hydraulic valve for release of the engagement between the taperedshoulders on the clamping sleeves and the tapered shoulders in thecontrol plunger, and so to release the engagement between the controlrod and the control plunger in the said limit positions.
 9. Hydrauliccontrol system according to claim 1, characterized in that thesupervisory unit has a trimming screw for adjustment of one limitposition of the control unit, thereby permitting, within certain limits,optional parallel linkage angles to which the toolholder is returnedafter tilting of the tool.
 10. Hydraulic control system according toclaim 1, characterized in that the regulating unit consists of aplunger, preferably acted upon by a spring, having at one end a holepassing axially through it and throttled by a disc.
 11. Hydrauliccontrol system according to claim 1 characterized in that the hydraulicvalve has hollow screws passing through it for pressure fluid and returnfluid to and from the control cylinders of the control arms and thehydraulic cylinder of the toolholder to permit manual adjustment of thepositions of control arms as well as toolholder, said hollow screwswithin the hydraulic valve having bushings leading to channels in thehydraulic valve.
 12. Hydraulic control system according to claim 11characterized in that, between channels for return fluid in thehydraulic valve and channels leading to one side of the controlcylinders, there is a nonreturn valve for the passing of fluid from thereturn channels to the control cylinders on movement of the control armsin a direction essentially coinciding with the direction of a forceacting upon the tool.
 13. Hydraulic control system according to claim12, characterized in that the hydraulic cylinder of the toolholder isallotted to a differential piston valve for transmission of fluid fromthe suction side to the pressure side of the hydraulic cylinder duringmovement of the tool in a direction essentially coinciding with thedirection of a force acting upon the tool.